Method of transmitting terminating call signals within a restricted duration and a base station and a portable unit for use in the same

ABSTRACT

A portable unit that may be called from a base station through a radio control channel by a succession of terminating call signals that is sent through the control channel from the base station to the portable unit for a first or restricted time duration (T 1 ), selected in consideration of a battery saving period of a battery saving operation carried out in the portable unit. Within the battery saving period, the portable unit is put into transient active and inactive states during a first time interval and a second time interval, respectively. Selection is made so that the first time duration is longer than the second time interval to receive at least one of the terminating call signals within the first time duration in the portable unit. The base station monitors an acknowledgement signal for a second time duration (T 2 ) after the lapse of the first time duration and interrupts the control channel when the acknowledgement signal is not received within the first and the second time durations. In the portable unit, the battery saving operation is released when the presence of the terminating call signals is detected by a squelch circuit.

This is a division of application Ser. No. 705,944, filed Feb. 26, 1985,now U.S. Pat. No. 4,679,244.

BACKGROUND OF THE INVENTION

This invention relates to a method of transmitting a terminating callsignals in a radiotelephone system and to a base station and a portableunit both of which are for use in the method. It is mentioned here thatthe portable unit may be a cordless telephone set, a handset, or thelike, and conveyed by a vehicle, such as a land mobile, or a person andthat the base station is fixed at a predetermined site and may thereforebe called a fixed station.

As a radiotelephone system, a multiple channel access system is knownwherein each of radio channels is used in common to a plurality ofportable units. The multiple channel access system is very effective inview of significant utilization of the radio channels. In the multiplechannel access system, a selected one of the radio channels is used totransfer a wide variety of control signals, such as a terminating callsignal, between the base station and the portable units and maytherefore be called a control channel. In this connection, the remainingchannels may be referred to as speech channels. From this fact, it isreadily understood that availability of the multiple channel accesssystem greatly depends on a length of occupied time in the controlchannel.

On the other hand, the portable unit comprises a receiver portion drivenby a battery. The receiver portion may not always be put into an activestate because occurrence of the terminating call signal is intermittentor spontaneous. Under the circumstances, a battery saver circuit isincluded in the portable unit in order to save power consumption of thebattery and to thereby extend a life time of the battery. Morespecifically, the battery saver circuit periodically puts the entiretyof the receiver portion into transient active and inactive states duringa first time interval and during a second time interval considerablylonger than the first time interval, respectively. In other words, abattery saving operation is carried out in the battery saver circuitduring the second time interval at a battery saving period. Preferably,the battery saving period is as long as possible in the light of savingof electric power of the battery.

In U.S. Pat. No. 4,419,765 issued to Wycoff et al, a receiver isdisclosed wherein the battery saving operation must intermittently beinterrupted after lapse of the first time interval to put the receiverportion into a receiving state when the terminating call signal isreceived during the first time interval. Thereafter, the intermittentinterruption of the battery saving operation is changed to a continuousinterruption when the terminating call signal is found to be destined tothe portable unit in question after detection of the terminating callsignal. Otherwise, the battery saving operation is restarted.

Let the terminating call signal be produced by the base station in theform of a succession of digital signals. In this event, the intermittentinterruption of the battery saving operation becomes objectionably longbecause the detection of the terminating call signal should be madethrough a filter with reference to at least one of the digital signalsuccession, for example, during a couple of the digital signalsuccessions. As a result, electric power of the battery might be wastedduring the intermittent interruption.

It is possible to reduce occurrence of the intermittent interruption byextending the battery saving period. However, it takes a long time toaccess the portable unit in question. This means that the controlchannel is occupied by the base station for a long time on production ofeach terminating call signal.

To the contrary, the intermittent interruption frequently occurs in theportable unit and results in serious consumption of the battery, whenthe battery saving period is shortened.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a method of transmitting aterminating call signal in a multiple channel access system, wherein anoccupied time of a control channel can be reduced on transmitting theterminating call signal.

It is another object of this invention to provide a base station for usein a method of the type described, which is capable of shortening theoccupied time of the control channel.

It is still another object of this invention to provide a portable unitwhich is for use in combination with a base station of the typedescribed and which can shorten an intermittent interruption of abattery saving operation.

A method to which this invention is applicable is for use in calling aportable unit from a base station through a radio control channel. Themethod comprises the steps of repeatedly producing in the base station aterminating call signal as a call signal succession, periodicallyputting the portable unit into transient active and inactive statesduring a first time interval and during a second time interval followingthe first time interval, respectively, and keeping the portable unitinto a continuous active state when one of the terminating call signalsis received during the first time interval. According to this invention,the method comprises the steps of measuring in the base station a firstduration longer than the second time interval and restricting productionof the call signal succession within the first duration.

According to an aspect of this invention, there is provided a basestation which is for use in the above-mentioned method and whichcomprises measuring means operable in relation to an incoming call formeasuring a first duration longer than the second time interval, signalproducing means coupled to the measuring means for iteratively producingelectric call signals representative of the terminating call signalsonly during the first duration, and sending means coupled to the signalproducing means for sending the electric call signals to the portableunit as the terminating call signals.

According to another aspect of this invention, there is provided aportable unit which is for use in combination with the base stationmentioned above and which comprises a controllable battery saver circuitfor putting the portable unit into the transient active and inactivestates and receiving means coupled to said battery saver circuit forcarrying out reception operation of radio signals including theterminating call signals. The portable unit further comprises meanscoupled to the receiving means for producing a presence signalrepresentative of presence of the terminating call signals and means forsupplying the presence signal to the battery saver circuit to make thecontrollable battery saver circuit release the battery saving operation.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a time chart for use in describing a conventional method ofcalling a portable unit from a base station;

FIG. 2 is a block diagram of a base station for use in a methodaccording to a preferred embodiment of this invention;

FIG. 3, depicted below FIG. 1, is a time chart for use in describing themethod mentioned in conjunction with FIG. 2; and

FIG. 4 is a block diagram of a portable unit for use in combination withthe base station depicted in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, description will be made in order to facilitate anunderstanding of this invention as regards a conventional method ofcalling a portable unit from a base station through a control one ofradio channels in a multiple channel access system. The remaining radiochannels may be referred to as speech channels.

As shown along the top line of FIG. 1, the portable unit is periodicallyput into a transient active state and a transient inactive state by abattery saver circuit (not shown, often indicated by BS) includedtherein when any signals are not received. The transient active andinactive states are repeated at a predetermined period which may becalled a battery saving period and which consists of a first and asecond time interval for the transient active and inactive states,respectively. Practically, the first time interval may be equal to onetenth of the second time interval, although the first time interval isexpanded in this figure for convenience of illustration. As a result,each battery saving period may almost be determined by the second timeinterval.

Inasmuch as the battery saver circuit is turned off during the transientactive state of the receiver or turned on during the transient inactivestate thereof, the first and the second time intervals may be alsocalled turnoff and turnon durations of the battery saving circuit,respectively. It is therefore readily understood that the battery savercircuit carries out battery saving operation only for the turnonduration of the battery saving circuit.

On the other hand, the base station is supplied with an incoming callthrough a subscriber line extended to an exchange. After detection ofthe incoming call, the base station repeatedly produces through theradio control channel a terminating call signal as a call signalsuccession. Each terminating call signal is modulated by a start code,an identification code, and a channel indication code all of which areshown in the art and which are given in the form of sequences of digitalsignals. The call signal succession lasts irrespective of the batterysaving period. In other words, the terminating call signals for eachincoming call are produced until a response is received from theportable unit, as will later be described.

The call signal succession is time sequentially delivered to theportable unit. It is assumed that each terminating call signal isdestined to the portable unit in question. Let the portable unit bechanged to the transient active state in course of reception of aspecific one TC of the terminating call signals. The specificterminating call signal TC is sent through a filter (not shown) to adiscriminator (not shown also) to detect whether or not the specificterminating call sigal TC is destined to the portable unit. In thisevent, the discriminator judges that the specific terminating call isnot destined or directed to the portable receiver because a whole of thespecific terminating call signal TC is not received. In other words, thediscriminator is not aware of arrival of the incoming call until thefollowing terminating call signal depicted at TC₁ arrives at theportable unit after the specific terminating call.

After discrimination of the following terminating call TC₁, the batterysaver circuit is released to put the entirety of the portable unit intoa continuous active state. When the following terminating call signalTC₁ carries no incoming call destined to the portable unit, the batterysaver circuit is turned on again to put the portable unit into thetransient inactive state. Anyway, the portable unit becomes active for along time in comparison with the transient active state because eachterminating call signal is usually longer than the first time interval.In other words, the battery saver circuit is turned off until thefollowing terminal call signal TC₁. Thus, the portable unit is kept inan active state after the transient active state. In other words, thebattery saver circuit should intermittently be interrupted after lapseof the first time interval. As a result, intermittent interruption ofthe battery saver circuit becomes long as described in the preamble ofthe instant specification.

After discrimination of the incoming call destined to the portable unit,an acknowledgement signal (ACK) is transmitted from the portable unit tothe base station in the manner known in the art.

Referring to FIG. 2, a base station is for use in a method according toa preferred embodiment of this invention and is connected to an exchange(not shown) through a subscriber line i a usual manner. The illustratedbase station comprises a station transmitter section 11, a stationreceiver section 12, and a station controller 13 coupled to both of thestation transmitter section 11 and the station receiver section 12 tocontrol both of them in the manner known in the art. The stationreceiver section 12 is similiar in structure to a conventional stationreceiver section. More specifically, the station receiver section 12comprises a station reception antenna 16 responsive to a radio inputsignal and a station receiver 17 coupled to the station receptionantenna 16 to produce a reception signal. A station squelch circuit 18monitors a reception state of the station receiver 17 by measuringintensity of a reception electric field. Supplied with a result ofmeasurement from the station squelch circuit 18, the station controller13 starts a reception operation. On the other hand, a station detector21 is operable to detect a reception control signal in response to thereception signal and to deliver the reception control signal to thestation controller 13. In addition, the reception signal is sent to afirst station amplifier 22 controlled by the station controller 13 andthereafter delivered to the exchange through a station hybrid 23 and thesubscriber line.

Referring to FIG. 3 together with FIG. 2, the station transmittersection 11 comprises a signal detector 26 for detecting a ringing signalof 16 Hz on reception of an incoming call IN from the exchange. When theringing signal of 16 Hz is detected by the signal detector 26, as shownalong the bottom line of FIG. 3, the station controller 13 begins toprocess the incoming call. A speech signal accompanied by the incomingcall is also sent through the station hybrid 23 and a second stationamplifier 27 to a transmitter 29 after detection of the ringing signalin a conventional manner.

The station controller 13 energizes a control signal producing circuit31 in response to the detection of the ringing signal to iterativelyproduce an electric control signal corresponding to the incoming callfor a first duration T₁ as shown along the bottom line of FIG. 3. Thefirst duration T₁ is selected in consideration of a battery savingperiod of a portable unit as will later be described with reference toFIG. 4.

In order to carry out the above-mentioned operation, the control signalproducing circuit 31 comprises a timer 33 enabled on detection of theringing signal for measuring the first duration T₁ and a control signalgenerator 35 for repeatedly generating the electric control signal onlyfor the first duration T₁ under control of the station controller 13.The electric control signal is supplied to the station transmitter 29set to the control one of the radio channels by the station controller13.

As a result, a succession of the electric control signals is transmittedas a succession of the terminating call signals from the stationtransmitter 29 through a transmission antenna 37 via the controlchannel.

From the above, it is readily understood that production of theterminating call signals is limited within the first duration T₁regardless of reception of an acknowledgement signal (ACK) to be givenfrom the portable unit. After lapse of the first duration T₁, thestation controller 13 forcibly interrupts the control channel when asecond duration T₂ lapses without reception of the acknowledgementsignal (ACK). Thus, when the first and the second durations T₁ and T₂lapse without reception of the acknowledgement signal, the stationcontroller 13 regards the incoming call as being abandoned.

Referring to FIG. 4 afresh and FIG. 3 again, the illustrated portableunit is for use in combination with the base station illustrated in FIG.2 and is put into transient active and inactive states during a firsttime interval and a second time interval during a waiting state for eachterminating call signal, as shown along the top line of FIG. 3. Thetransient active and inactive states may be, for example, 70milliseconds and 630 milliseconds long, respectively, and repeated at abattery saving period of, for example, 700 milliseconds.

More particularly, the portable unit illustrated in FIG. 4 comprises aunit receiver section 41 operable in a manner to be described later, aunit transmitter section 42 operable in a manner similar to that of theconventional portable unit, and a unit controller 43 for controllingboth of the unit receiver section 41 and the unit transmitter section42.

The unit receiver section 41 comprises a battery saver circuit 45coupled to the unit controller 43 for periodically producing an electricsource voltage V under control of the unit controller 43 at the batterysaving period. The electric source voltage V is produced for the firsttime interval and stopped for the second time interval. Under thecircumstances, let the terminating call signals be repeatedly deliveredfrom the base station to the portable unit, as illustrated along thebottom line of FIG. 3. Each terminating call signal may last, forexample, 200 milliseconds.

During the transient inactive state, no terminating call signal isreceived by the unit receiver section 41. In FIG. 3, a particular oneTC_(a) of the terminating call signals arrives at a unit receptionantenna 46 and is sent to a unit receiver 47 when the transient inactivestate is released. The unit receiver 47 comprises a high frequencyamplifier, mixers, an intermediate frequency amplifier, and an FMdemodulator, in the manner well known in the art, and is set to thecontrol channel during the waiting state. In the example beingillustrated, an intermediate output signal is delivered from theintermediate frequency amplifier to a squelch circuit 48 for measuring afield intensity of the control channel during the waiting state. Whenthe squelch circuit 48 detects presence of the terminating call signalson release of the transient inactive state, the squelch circuit 48supplies the unit controller 43 and the battery saver circuit 45 with apresence signal representative of presence of the terminating callsignals before the next following terminating call signal TC_(b) isreceived by the unit receiver section 47.

Responsive to the presence signal, the battery saver circuit 45 releasesthe battery saving operation at a time instant t₁ to put the unitreceiver section 41 into the active state. Under the circumstances, thenext following terminating call signal TC_(b) is sent through the unitreceiver 47 to a control signal detector 51. The start, theidentification, and the channel indication codes are detected from thenext following terminating call signal TC_(b) to be delivered to theunit controller 43. A combination of the unit controller 43 and thecontrol signal detector 51 may be referred to as a detection circuit fordetecting the terminating call signals.

It should be noted here that the base station produces the terminatingcall signals only for the first duration T₁ as mentioned in conjunctionwith FIG. 3. Inasmuch as one of the terminating call signals should bereceived within the first duration T₁ by the portable unit, the portableunit must be put into the transient active state at least one timewithin the first duration T₁. For this purpose, the first duration T₁for the call signal succession is selected so that it becomes longerthan the second time interval for the transient inactive state. Inasmuchas the battery saving operation of the battery saver circuit 45 israpidly released or rendered inactive upon detection of presence of theterminating call signals as mentioned before, the first duration T₁ maybe longer than the second time interval by a third duration for a singleone of the terminating call signals. Practically, the first duration T₁is equal to 3.6 seconds in order to reduce the loss probability. Theterminating call signals are therefore produced eighteen times for thefirst duration.

Let the unit controller 43 judge that the next following terminatingcall is destined to the portable unit in question. In this event, theunit controller 43 sets a unit transmitter 53 to the control channel anddrives a control signal producing circuit 55 and puts the battery savercircuit 45 into a continuous inactive state. As a result, the unitreceiver section 41 is brought into the continuous active state. Thecontrol signal producing circuit 55 sends the acknowledgement signal(ACK) through the unit transmitter 55 and a unit transmission antenna 56to the base station. Simultaneously, the unit receiver 47 switches fromthe control channel to one of the speech channels that is specified bythe channel indication code.

In FIG. 2, the base station is put into the waiting state of theacknowledgement signal for the second duration T₂ after lapse of thefirst duration T₁, as mentioned before. The second duration T₂ may be,for example, 200 milliseconds. When the acknowledgement signal (ACK) isreceived within the first and the second durations T₁ and T₂, thestation controller 13 makes the station transmitter 29 change thecontrol channel to the one speech channel. Thus, a speech signal can besent from the exchange to the station transmission antenna 37 throughthe station hybrid 23, the second amplifier 27, and the stationtransmitter 29. Likewise, another speech signal is sent in the portableunit from a transmitter set 57 to the unit transmitter 53 through atransmitter amplifier 58.

In the portable unit, the speech signal is received by the unitreception antenna 46 and sent through the unit receiver 47 and areceiver amplifier 61 to a receiver unit 62 and reproduced by thereceiver unit 62. Thus, communication is carried out between the basestation and the portable unit.

Let the acknowledgement signal (ACK) be not received by the base stationwithin the first and the second durations T₁ and T₂. In this event, thestation controller 13 regards the incoming call as being abandoned andmakes the station transmitter 29 forcibly interrupt the control channel.Thus, the station transmitter 29 serves to interrupt the controlchannel.

On the other hand, if no speech signal is received by the portable unitfor a preselected duration after transmission of the acknowledgementsignal, the unit receiver 47 switches the one speech channel to thecontrol channel under control of the unit controller 43. Thus, theportable unit returns back to the waiting state.

As mentioned above, the control channel is occupied by the terminatingcall signals only for the first duration. It is therefore possible toimprove availability of the control channel. In addition, the batterysaving operation of the battery saver circuit 45 is released bydetecting presence of any terminating call signal by the squelch circuit48 before decoding the terminating call signal. Thus, the battery savingoperation is controlled in the portable unit with reference to both ofthe field intensity and the presence signal representative of presenceof any digital data signals. A time interval for detecting the fieldintensity may be shorter than 0.5 millisecond. Accordingly, it ispossible to shorten a duration for the active state of the unit receiversection 41 and to therefore save power consumption of the battery. Inaddition, detection of the digital data signals serves to establish bitsynchronism and to insure accuracy of detection.

While this invention has thus far been described in conjunction with apreferred embodiment thereof, it will readily be possible for thoseskilled in the art to put this invention into practice in various othermanners. For example, the receiver antennas 16 and 46 may be common tothe transmitter antennas 37 and 56, respectively.

What is claimed is:
 1. A portable unit responsive to a sequence ofterminating call signals repeatedly supplied to said portable unit andperiodically put by a controllable battery saver circuit into transientactive and inactive states during a first time interval and during asecond time interval following said first time interval with batterysaving operation transiently released and carried out in said batterysaver circuit, respectively, said portable unit being kept in acontinuous active state when one of said terminating call signals isreceived during said first time interval and comprising receiving meanscoupled to said battery saver circuit for carrying out receptionoperation of radio signals including said terminating call signals,wherein the improvement comprises:means coupled to said receiving meansfor producing a presence signal representative of the presence of saidterminating call signals by measuring an intensity of said radiosignals; and means for supplying said presence signal to said batterysaver circuit to make said controllable battery saver circuit releasesaid battery saving operation.